This invention relates generally to a liquid crystal texture transformation system and more particularly to imaging systems wherein an imaging member comprises an optically negative liquid crystalline composition.
Liquid crystalline substances exhibit physical characteristics some of which are typically associated with liquids and others which are typically unique to solid crystals. The name "liquid crystals" has become generic to subtances exhibiting these dual properties. Liquid crystals are known to appear in three different forms: the smectic, nematic and cholesteric forms. These structural forms are sometimes referred to as mesophases thereby indicating that they are states of matter intermediate between the liquid and crystalline states. The three mesophase forms of liquid crystals mentioned above are characterized by different physical structures wherein the molecules of the compound are arranged in a manner which is unique to each of the three mesomorphic structures. Each of these three structures is well known in the liquid crystal art.
Cholesteric liquid crystals are known to exhibit various observable textures. For example, cholesteric liquid crystalline materials may adopt a homeotropic, a focal-conic or a Grandjean plane texture as modifications of the cholesteric mesophase itself as is described in Molecular Structure and the Properties of Liquid Crystals, Gray, G. W., Academic Press, London, 1962, pp. 39-54.
It is known in the art that a cholesteric liquid crystalline material in the Grandjean texture state may be transformed to the focal-conic texture state by application of D.C. electrical fields or by relatively low frequency A.C. electrical fields. For a detailed description of this advantageous method see U.S. Pat. No. 3,642,348 to Wysocki et al. It has further been disclosed that a cholesteric liquid crystalline material in the focal-conic texture state may be transformed to the Grandjean texture state by the application of relatively high frequency A.C. electrical fields. A detailed description of this method is provided in U.S. Pat. No. 3,680,950 to Haas et al.
It is also known in the art that an optically negative liquid crystalline material may be transformed to the optically positive state by the application of electrical fields. See, for example, U.S. Pat. No. 3,652,148 to Wysocki et al. There are also disclosed systems for obtaining this result wherein the optically negative liquid crystalline material includes an additive of electrophoretic-like or dipolar material dispersed therein. For an extensive description of this type of system see U.S. Pat. No. 3,697,150 to Wysocki.
The present invention relates to a texture transformation system in which an optically negative liquid crystalline composition is transformed from the focal-conic state to the Grandjean texture state by means of an applied electrical field.